European Perspectives
Authors: Matthias Gutberlet, Sandra Erbs, P Courtesy
Journal: Circulation (2006)

D uring the past 10 years I have worked with cardiac multi-detector computed tomography (MDCT), singlepositron-emission CT (SPECT), positron-emission tomography (PET), and echocardiography, although I am now working mainly with magnetic resonance imaging (MRI).MRI has already proved itself as the modality of choice for the assessment of cardiac volumes, global function, and muscle mass.It is especially important for the assessment of the right ventricle, which is significant in congenital heart disease.This application is especially relevant to me, as I am one of the leaders for MRI in the Competence Network for Congenital Heart Defects project, sponsored by the German Federal Ministry of Education and Research. Imaging Technologies Reduce Invasive Diagnostic AngiogramsWhen it comes to the assessment of cardiac anatomy, MRI has to compete with MDCT, a technique that at the moment has the edge in the delineation of the coronary vessels.In its favour, MRI facilitates the differential diagnosis of a wide range of cardiomyopathies because of its superiority for tissue characterisation.It has also become the method of choice for assessing myocardial viability, because it offers better spatial resolution compared to nuclear medicine techniques like SPECT and PET.I believe it also has serious potential to become the best method for the evaluation of myocardial perfusion.This is of vital importance, because everyone wants to reduce the number of unnecessary catheter angiograms (CAs).CA is an invasive procedure, and it is clearly undesirable to use it for diagnosis in cases where it turns out that no therapeutic intervention is necessary.In the United States, coronary artery disease is assessed with noninvasive imaging technologies, principally SPECT.According to the 2003 Nuclear Medicine Census Database of IMV, a medical information company from Des Plaines, Ill, the number of cardiac SPECT procedures performed is increasing steadily in the United States. 1 In Europe, the number is also expanding, but more slowly.This means that other noninvasive imaging modalities like stress-MRI or stress-echocardiography play a more important role.Reduced perfusion is the first step on the ischaemic cascade; abnormalities in wall motion follow later.So an imaging modality like SPECT or PET that reliably detects perfusion abnormalities has the great advantage, at least in theory, of allowing the clinician to detect the disease at an earlier stage.MRI, or, with certain limitations, stressechocardiography, is useful in assessing myocardial perfusion under stress-induced ischaemia.Both these techniques, especially the latter, need further validation.Inducing stress to assess coronary artery disease may be done in a number of ways, physical or pharmacological.Stress for perfusion studies is usually induced using adenosine.The fact that this drug has a short half-life makes it attractive and easy to control, and this is especially important in the MR environment, in which monitoring of the patient (with an ECG, for example) can be difficult due to the interference of the magnetic field.However, cardiologists trained in stressecho may find the MRI's visual wall-motion analysis using dobutamine more robust and easier to analyse, although it takes longer to induce stress than using adenosine. MR Versus Other Imaging Technologies in the Assessment of Cardiac PerfusionTechnetium SPECT, a robust, well-standardised technique with a track record spanning more than 3 decades, is the principle competition.In contrast to MRI, straightforward "eyeballing" gives reasonable results.But false positives due to attenuation caused by the diaphragm, the breasts, or adipose tissue in obese patients can be a problem.This can be corrected with the latest technology, which is not always available.Furthermore, the spatial resolution of SPECT is limited, and poor compared to MRI.These disadvantages are in addition to the risks associated with radiation exposure; the absence of such risks is one of the major advantages of MRI over nuclear medicine.Against MRI, it has to be said that it can be time-consuming